Barriers to Quantitative Electron Probe X-Ray Microanalysis for Low Voltage Scanning Electron Microscopy

Low voltage x-ray microanalysis, defined as being performed with an incident beam energy ≤5 keV, can achieve spatial resolution, laterally and in depth, of 100 nm or less, depending on the exact selection of beam energy and the composition of the target. The shallow depth of beam penetration, with the consequent short path length for x-ray absorption, and the low overvoltage, the ratio of beam energy to the critical ionization energy, both contribute to minimizing the matrix effects in quantitative x-ray microanalysis when the unknown is compared to pure element standards. The low beam energy restricts the energy of the atomic shells that can be excited, forcing the analyst to choose unfamiliar shells/characteristic peaks. The low photon energy shells are subject to low fluorescence yield, so that the peak-to-continuum background is reduced, severely limiting detectability. The limited resolution of semiconductor energy dispersive spectrometry results in frequent peak interference situations and further exacerbates detection limits. Future improvements to the x-ray spectrometry limitations are possible with x-ray optics-augmented wavelength dispersive spectrometry and microcalorimeter energy dispersive spectrometry.     

Accurate Cross Sections for Microanalysis

To calculate the intensity of x-ray emission in electron beam microanalysis requires a knowledge of the energy distribution of the electrons in the solid, the energy variation of the ionization cross section of the relevant subshell, the fraction of ionizations events producing x rays of interest and the absorption coefficient of the x rays on the path to the detector. The theoretical predictions and experimental data available for ionization cross sections are limited mainly to K shells of a few elements. Results of systematic plane wave Born approximation calculations with exchange for K, L, and M shell ionization cross sections over the range of electron energies used in microanalysis are presented. Comparisons are made with experimental measurement for selected K shells and it is shown that the plane wave theory is not appropriate for overvoltages less than 2.5 V.     

The x-ray astronomy experiment

One of the scientific experiments onboardAryabhata was designed to detect and measure celestial x-rays in the energy range 2.5–155.0 keV. The payload systems comprising proportional counter and scintillation counter, telescopes were intended for observations in the pointed and scan modes respectively for investigating the emission properties of celestial x-ray sources. The paper presents the details of these telescopes, their inflight performance as well as the nature of the data obtained during the first few orbits.     

高能 X 射线工业 CT 技术的研究进展

目的 研究分析了国内外高能X射线工业CT技术的进展情况，方法 通过有关文献资料，对目前国际上主要的高能X射线工业CT技术及设备进行评述。结果和结论 对美国、德国等发达国家的高能X射线工业CT设备、线阵探测器、面陈探测器及重建算法进行了分析。     

Sophisticated equipment developed for growth and evaluation of perfection of nearly perfect crystals

This paper reviews four major equipment developed at the National Physical Laboratory for growth and perfection evaluation of single crystals, namely (i) a crystal puller for growth of nearly perfect crystals by the Czochralski method; (ii) a microfocus x-ray generator; (iii) an x-ray diffraction topography camera; and (iv) a triple crystal x-ray diffractometer. The crystal puller can provide smooth, uniform and variable pulling rates. The maximum length of pull is nearly 60cm. Efforts have been made to isolate vibrations. Nearly perfect single crystals of KCl, KBr and NaCl with maximum diameter of ∼ 60 mm have been grown. The crystals give diffraction curves with half width in the range of 10–30 sec of arc. In the projection topographs, dislocations can be resolved and characterized. The microfocus x-ray generator is a demountable continuously evacuated system with specially designed electron gun and anode assembly. The vacuum is continuously monitored for ease of maintenance. In the point focus mode the spot size is 40 μm on the anode. X-ray topography system is a versatile equipment used for projection and section topography. It can provide 360° rotations to the specimen disc around an axis perpendicular to it. Rotations of a few sec of arc can be given to the specimen around a vertical axis. Typical diffraction curves of a dislocation-free crystal and a crystal with boundaries are shown. Well-resolved images of dislocations are shown in a topograph as an illustration. In the triple crystal x-ray diffractometer a highly collimated and monochromated Kα₁ exploring x-ray beam is obtained by combining microfocus source, a special collimator and crystal monochromators of Bonse-Hart type. With this beam very narrow diffraction curves with half width of about 5 sec of arc can be recorded. Typical results of measurement of diffuse x-ray scattering (dxs) on nearly perfect silicon single crystals are discussed. It has been observed that the contribution of phonons to thedxs is negligible. Thedxs is mainly due to point defect aggregates.     

Preparation and characterization of Pb1−x Sn x Te pseudobinary alloy semiconductors

Ap-type pseudo-binary alloy semiconductor, Pb_0·3Sn_0·7Te, has been prepared fromp-type specimens of PbTe and SnTe and lattice constants determined with an accuracy of 0.0001 nm. Vacuum annealing of Pb_0·3Sn_0·7 Te reveals two new x-ray powder diffraction lines bearing indices (444) and (800), while others become more sharp, CuK_a-doublets get clearly resolved and the lattice constant is increased by ∼ 0·0002 nm. Slight deviation from Vegard’s law linearity is observed showing that the sample must be considered as ternary in nature. Thin films deposited on mica and glass substrates kept at room temperature are found to have a little higher SnTe content. The effective carrier concentration calculated from Hall measurements at room temperature is ∼ 3·4×10²⁶ m⁻³.     

Structural,Conductivity, and Dielectric Relaxation Studies of La0.9Ba0.1GaO3-δ System

La_0.9Ba_0.1GaO_3-δ has been synthesized through solid-state reaction method. X-ray diffraction, AC conductivity, and scanning electron microscopy are used to investigate the structural properties and morphology of the system. X-ray refinement indicates that LaGaO₃ is the major phase having an orthorhombic structure with the space group Ibmm. The study revealed that the Ba-dopant in the LaGaO₃ creates oxygen vacancies, which are responsible to increase the ionic conductivity through hopping mechanism. The activation energy of the system is nearly ～0.65 eV. It indicates that the major contribution to overall conductivity is ionic in the present system. The impedance behavior of the sample with frequency and temperature has been investigated using the Bode's plots. The loss tangent variation with temperature has been plotted to verify the relaxation behavior of the present system.     

Structural studies of copper sulfide films: effect of ambient atmosphere

Abstract

We examined the structural properties of copper sulfide films as a function of the sulfurization time of 70-nm-thick Cu films. Copper sulfide films with various phases such as mixed metallic Cu-chalcocite, chalcocite, roxbyite, and covellite phases were formed with increasing sulfurization time. To evaluate the structural stability of various films, all the films were exposed to the ambient atmosphere for the same amount of time. Although the phase structure and stoichiometry of the films were maintained at a greater depth, the near-surface region of the films was oxidized and covered with overlayers of oxide, hydroxide, and/or sulfate species due to the exposure and reaction with the ambient atmosphere. The oxygen uptake and its reactivity with the copper sulfide film surfaces were enhanced with increasing sulfur content of the films. In addition, the type of divalent state of copper formed on the film surfaces depended on the phase structure, composition, and stoichiometry of the films.     

Phase transformations in sputtered Ni-Mn-Ga magnetic shape memory alloy thin films

Ni-Mn-Ga magnetic shape memory alloy films have been prepared by the DC magnetron sputtering technique. As-deposited films show a quasi-amorphous structure that crystallizes at ~ 500 K. Crystallization study using Kissinger's analysis reveals a relatively low activation energy indicating partial crystallinity in the films. In situ X-ray diffraction studies show reversible martensite phase transformations, and phase segregation to non-transforming L1₂ precipitates at higher temperatures. It was observed that the phase segregation can be suppressed by low temperature heat treatment.     

Measurement of the Parameters of the Focal Spot of an x-Ray Tube Using Kumakhov Optics

A technique of determining the parameters of the focal spot of an x-ray tube by obtaining its image by means of Kumakhov optics is described. Through the use of the image thus obtained, it is possible to determine the size and shape of the effective focal spot. Results of investigations of different x-ray tubes are presented.     

Comparison of the NIST and ENEA Air Kerma Standards

A comparison was made between the National Institute of Standards and Technology (NIST) and Ente per le Nuove Tecnologie l’Energia e l’Ambiente (ENEA) air kerma standards for medium energy x rays and ⁶⁰Co gamma rays. The comparison took place at ENEA in June 1994. Two different transfer chambers from NIST were used for the comparison. The measurements were made at radiation qualities similar to those used at the Bureau International des Poids et Mesures (BIPM) (generating voltages of 100 kV, 135 kV, 180 kV and 250 kV, respectively) and with ⁶⁰Co gamma radiation. The transfer chamber calibration factors obtained at the NIST and at the ENEA agreed with one another to 0.03 % for ⁶⁰Co gamma radiation and between 0.1 % to 0.8 % for the medium energy x-ray beam codes.     

X-Ray Microanalysis in the Variable Pressure (Environmental) Scanning Electron Microscope

Electron-excited x-ray microanalysis performed in the variable pressure and environmental scanning electron microscopes is subject to additional artifacts beyond those encountered in the conventional scanning electron microscope. Gas scattering leads to direct contributions to the spectrum from the environmental gas, as well as remote generation of x rays by electrons scattered out of the focussed beam. The analyst can exert some degree of control over these artifacts, but depending on the exact situation, spurious elements can appear at the trace (< 0.01 mass fraction), minor (0.01 mass fraction to 0.1 mass fraction), or even major (> 0.1 mass fraction) levels. Dispersed particle samples give the least compromised results, while fine scale microstructures are the most severely compromised. Procedures to optimize the situation based upon specimen preparation as well as spectral processing are described.     

Statistics of High Purity Nickel Microstructure From High Energy X-ray Diffraction Microscopy

We have measured and reconstructed via forward modeling a small volume of microstructure of high purity, well annealed nickel using high energy x-ray diffraction microscopy (HEDM). Statistical distributions characterizing grain orientations, intra-granular misorientations, and nearest neighbor grain misorientations are extracted. Results are consistent with recent electron backscatter diffraction measurements. Peaks in the grain neighbor misorientation angle distribution at 60 degrees (∑3) and 39 degrees (∑9) have resolution limited widths of ≈ 0.14 degree FWHM. The analysis demonstrates that HEDM can recover grain and grain boundary statistics comparable to OIM volume measurements; more extensive data sets will lead to full, five parameter grain boundary character distributions. Due to its non-destructive nature, HEDM can then watch, both statistically and through tracking of individual grains and boundaries, the evolution of such distributions with processing of the sample.     

Variable Magnification With Kirkpatrick-Baez Optics for Synchrotron X-Ray Microscopy

We describe the distinction between the operation of a short focal length x-ray microscope forming a real image with a laboratory source (convergent illumination) and with a highly collimated intense beam from a synchrotron light source (Köhler illumination). We demonstrate the distinction with a Kirkpatrick-Baez microscope consisting of short focal length multilayer mirrors operating at an energy of 8 keV. In addition to realizing improvements in the resolution of the optics, the synchrotron radiation microscope is not limited to the usual single magnification at a fixed image plane. Higher magnification images are produced by projection in the limit of geometrical optics with a collimated beam. However, in distinction to the common method of placing the sample behind the optical source of a diverging beam, we describe the situation in which the sample is located in the collimated beam before the optical element. The ultimate limits of this magnification result from diffraction by the specimen and are determined by the sample position relative to the focal point of the optic. We present criteria by which the diffraction is minimized.     

Electron microscopy of layered single crystals grown by direct vapour transport method

Besides interesting properties such as optical, transport, structure, etc. possessed by crystals of transition metal dichalcogenides, they have also been found to have a potential application in the fabrication ofpec solar cells. These crystals are normally grown by carrier gas transport technique but are always contaminated by carrier gases. A new method of direct vapour transport has been developed and successfully applied to grow these crystals including those of off-stoichiometric varieties. The crystals thus grown have been characterized structurally using the techniques of x-ray powder, rotation and Weissenberg photographs and electron diffraction. Perfection studies have been made by techniques like chemical etching and electron microscopy. This review describes the electron microscopic studies made on the single crystals of the layered compounds. High resolution technique of weak beam has been employed to study dislocation pattern. Dissociated dislocations have been used to estimate stacking fault energy. Such measurements have also been carried out at different temperatures and the variation of stacking fault energy with temperature has been worked out. Interesting information regarding phase transformation for TaS₂ and W₃Se₄ in the temperature range 109 to 580 K has been derived from the electron diffraction studies and the implications have been discussed.     

Characterisation of high purity rare-earth oxides by x-ray fluorescence methods

X-ray fluorescence methods for the determination of individual rare earth impurities in high purity rare earth oxidesviz., Y₂O₃, La₂O₃, CeO₂, Pr₆O₁₁, Nd₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Tb₄O₇, Dy₂O₃, Ho₂O₃ and Er₂O₃ have been developed in our laboratory. The samples are converted to oxalate form and double-layer pellets are prepared using boric acid as binding material. A semiautomatic x-ray spectrometer is used for the analyses. Choice of instrumental parameters and analysis lines is discussed. The determination range varies from 0.005% to 1.0% for most elements with good precision and adequate accuracy.     

Analytical electron microscopy of aluminium alloys

X-ray microanalysis and electron energy loss spectroscopy of thin foils constitute the important techniques of high resolution chemical analysis using the electron microscope. The technique of x-ray microanalysis is discussed in this paper with particular emphasis on the study of aluminium alloys using a dedicated scanning transmission electron microscope (stem). The principle of determining chemical composition from observed x-ray peak intensities including the absorption of x-rays and beam broadening in thin foils are considered. The accuracy of peak intensity measurement and detection limits in x-ray microanalysis are illustrated with reference to Al-Mn alloys. The Cliff-Lorimer (k) factors for manganese, iron and copper with respect to aluminium were obtained from standard samples. Identification of phases in 1100 and 1200 aluminium and 3008 (Al-Mn-Zr) alloy were carried out from measured intensities of x-ray peaks. The experimental results emphasize the value of developing techniques for extracting the particles from the aluminium matrix. The transition phases formed in Al-6%Zn-3%Mg and Al-4% Cu were investigated by micro-diffraction and x-ray microanalysis.     

Three dimensional strain measurements with x-ray energy dispersive spectroscopy

A feasibility study was performed to show the ability of energy dispersive x-ray diffraction (EDXRD) to measure three dimensional strain distributions in thick industrial materials. Photon energies up to 130 keV were used to guarantee penetration through the sample and curve fitting techniques applied to peak position determination. This system was used to measure the strain gradient through the thickness of a 9.5 mm thick cantilevered steel bar.     

Measurement of the characteristics of a point source of x-rays using a picosecond laser plasma

The emissive properties of silicon and aluminum plasmas, produced by 40 psec laser pulses with a peak intensity of greater than 10¹⁴ W/cm², are investigated. The x-ray line spectra of H- and He-like ions, measured with high resolution, are analyzed to determine the plasma parameters. The form of the resonance lines and their intensity with respect to the corresponding dielectronic satellites and the intercombination line are compared with model calculations.Translated from Izmeritelnaya Tekhnika, No. 1, pp. 50–55, January, 2005.     

Diffractive Optics From Self-Assembled DNA

An algorithm is presented for assembling tiles into a variable spaced grating, the one-dimensional analog of a Fresnel zone plate. The algorithm supports multi-level gratings. The x-ray properties of such a grating, assumed to be constructed from DNA are estimated, leading to the conclusion that thick structures may be useful for intermediate energy x rays, but that thin structures for soft x rays are best used as disposable masks. The diffraction of cold, coherent atoms is a plausible application for single layer stencils.